Disposable filtration cartridges for filtering fluids, such as engine oil, are well known in the art. Most of these filter cartridges utilize the well-known "spin-on, spin-off" connection construction. With these known constructions, however, the filter cartridge is permanently sealed in its housing and the entire filter including the housing, must be discarded and replaced after use because such a procedure is costly and wasteful and poses an environmental problem due to the difficulty associated with disposing of the spent filter cartridge.
To reduce the costs associated with replacing both the filter element and the support housing, and to minimize the environmental impact associated with that disposal, filters with removable filters have been developed. One such filter is disclosed in U.S. Pat. No. 4,128,324. In that patent, a tubular metal support member is used in conjunction with the filter element to facilitate disassembly and replacement of component parts within large industrial filters. But the construction disclosed in U.S. Pat. No. 4,128,324 is directed to large, high-cost industrial filters and fails to address the requirements of the lower-cost "spin-on, spin-off" construction and is therefor entirely silent with respect to how the filter cartridge and associated support are connected to, and supported by, the outer housing to facilitate ease of disassembly.
Other inventors have addressed the issue of how to easily remove a filter cartridge from the filter housing. In the system disclosed in published application WO96/09875, a spring-assist mechanism is used as part of the locking assembly which secures the filter within the housing but also provides for the disassembly from and the removal of, the cartridge from its canister housing. In that application, an annular filter is coupled with a closure plate upon which a spring element exerts an axial pressure in order to secure the filter in place within the canister.
Although the design disclosed in WO96/09875 utilizes stiffening support rings attached along the axis of the filter to support the pleated filter element, these rings do not support the filter against the axial force exerted by the spring or the local fluid pressures caused by the inward or outward flow of the liquid being filtered. This lack of such support is critical when delicate filter media is employed because the dangers of buckling, collapsing, or blow-through is much greater with this type of material. Ultimately, and owing to these dangers, the usefulness of the filter apparatus disclosed in WO96/09875 is questionable in many applications, involving the separation of fine particles.
Accordingly, one object of the present invention is to provide a multi-media filtration system which utilizes a standard "spin-on, spin-off" design, and which is capable of separating the finest of particles, including particles at the micron and sub-micron level, yet provides the convenience of a reusable and remountable filter system adaptable to a filter head or block in which all of the components may be reused except for any disposable filter element.
Another object of the present invention is to provide a spin-on filter assembly that incorporates a reusable center tube support which serves to position the filter element within the filter housing and to support the filter media against the hydraulic pressures being asserted by the fluid being filtered so as to minimize buckling, collapse, or blow-through and to isolate the filter media from other internal forces.
Related objects and advantages of the present invention will also be apparent from review of the following description and appended claims.